The conventional common rail fuel injection apparatus has the problem of causing problems in the operation of injecting fuel from the injectors. One of these is that when fuel injection is abruptly terminated because, for instance, the driver has taken his or her foot off the accelerator pedal to invoke engine braking effect, the rail pressure rises to above the desired pressure so that when fuel injection is resumed, high-pressure fuel is injected at one time within a short period. Japanese Unexamined Patent Publication No. Hei 11(1999)-173192, for example, teaches a configuration for overcoming this drawback by utilizing the fact that a delay arises between the time when the solenoid valve of an injector operates and the time when the valve body actually lifts to assume the valve-open state, i.e., by opening the solenoid valve of the injector in the course of this delay for a time period shorter than the delay, thereby spilling high-pressure fuel in the common rail to the low pressure side through the solenoid valve and lowering the rail pressure, without conducting fuel injection into the cylinder from the injector.
With this proposed configuration, however, the solenoid valve opening operation for lowering the fuel pressure in the common rail using the solenoid valve of the injector must be effected under very restricted conditions and, moreover, the fuel must be spilled within a period even shorter than the short period of about several msec during which the solenoid valve of the injector opens the valve body. Problems therefore exist in the points that the reduction rate of the rail pressure is difficult to increase, that when the operating state of the engine changes radically, it is hard to keep up by lowering the rail pressure to appropriate values, and that cases frequently arise in which optimum combustion cannot be achieved in the cylinder.
An object of the present invention is to provide a common rail fuel injection apparatus that enables the foregoing problems in the prior art to be solved.
Another object of the present invention is to provide a common rail fuel injection apparatus that enables reduction of rail pressure to be conducted rapidly.
Another object of the present invention is to provide a common rail fuel injection apparatus that enables fuel injection operation to be conducted stably.